A major aspect of global warming is ocean acidification. To provide a baseline for future change, investigators have been able to track the geological record of ocean acidification back to 300 million years ago (mya). One of the key factors is tracing the history of boron isotopes. The principal low frequency sound absorption mechanism in seawater is a boron reaction which is pH dependent (the lower the pH, the lower the absorption), so this geological record can be used to estimate sound absorption in the ocean all the way back to the carboniferus period. The broad picture is that low frequency absorption in the ocean decreased from 300 mya to 200 mya, was relatively constant from 200 mya to 100 mya, and then has been increasing since. The present level is back to one similar to that 300 mya. Future global warming may reverse this trend and cause the absorption to decrease down to a level similar to when the dinosaurs roamed (100 mya).